Upgrade to upstream release 0.28.2

This upgrades to the latest 0.28.2 release. I did a gbp import-orig --uscan and rebased patches with gbp pq rebase. I had some trouble with sphinx and a failing cython test but this has resolved with upgrades of dependencies. On my latest run, gbp buildpackage completed, running Cython's tests without errors. Strangely, one of Cython's tests is now failing again.

I am not terribly experienced with Debian development, so I might be missing very obvious things, please let me know :)

From my point of view, the following still needs to be done:

• gbp pq rebase added some headers to the patches. Is that in principle Ok?
• I need to fix the added Date: headers in the patches.
• gbp pq rebase dropped a patch for squeeze. Is that Ok?
• Cython 0.28 is not fully compatible with 0.26 (one thing I am aware of: some dubious things that used to sort-of-work in 0.26 are now errors.) Do we need to do something about this?
• Do I need to create MRs for upstream and pristine-tar (and the new upstream tag) as well?
• Fix End-to-end scanner_trace test. Or maybe this can be postponed since it does happen only to me and it is not a new problem?